1. Technical Field
The invention relates to an alarm device containing a condition sensor element which, upon occurrence of a condition which is to be reported, alters its output potential or voltage, so that there is produced an alarm signal.
2. Field of Use of the Invention
Such alarm devices can be used for reporting undesired conditions or phenomena, for instance for detecting fires, the presence of dangerous gases or vapors, undesired temperature increases, or for intrusion protection purposes. The signal which is reported back can be employed as an alarm signal or for initiating protective or counter measures upon occurrence of the undesired condition or phenomena.
The sensor elements which are employed in the alarm device are tuned to the condition which is to be detected and, for instance, are structured as fire, smoke, gas, radiation, temperature or intrusion detectors. The invention can be particularly used to advantage in those applications where there are required sensor elements having high electrical resistance, for instance for ionization chambers used as fire detectors or alarms.
3. Prior Art
With heretofore known alarm installations the voltage supply is accomplished from an evaluation device to the individual alarm devices arranged remotely therefrom and reporting-back of the signal from such alarm devices to the central signal station, as a rule, is accomplished by means of electrical lines or conductors, if desired, also by wireless electrical transmission. However, such type transmission is extremely prone to disturbances and unreliable. When utilizing line transmission frequently electrical disturbances arise, for instance, network or mains pulses or electrical voltages are induced in the lines, which can lead to spurious response of the alarm devices and to faulty signal transmission. Due to the voltage drop in the lines the supply voltage fluctuates, so that complicated stabilization devices are needed. The components of the alarm devices are furthermore exposed to the effects of the environment, for instance are temperature-dependent, so that it is necessary to undertake complicated compensation measures. In special fields of application, especially in explosion-endangered environments, there are required further special protective measures when the infeed of the voltage occurs by means of the electrical lines. When using a wireless transmission technique and a special explosion-protected design of the alarm devices it is possible to overcome the last-mentioned drawback, yet as is well known wireless transmission is appreciably more prone to disturbances and less reliable because of the multiplicity of disturbances which can arise.